The present invention relates to the identification and characterization of particulate substances, and particularly substances which can be maintained in a static suspension.
It is known that such substances, for example those constituted by biological particles in static suspension, can be identified by subjecting such a suspension to modulated, collimated, monochromatic radiation, modulating and detecting the resulting scattered radiation, and then determining the intensities of various frequency components of the detected radiation, which components correspond to selected elements of a Mueller matrix.
The Mueller matrix is a 4.times.4 matrix which describes the polarization sensitive transformation of an incident beam of light into a scattered beam of light by a scattering object such as a particle or a suspension of particles. Much information concerning the internal structure and shape of such particles can be derived about the scattering particles from the simultaneous determination of multiple Mueller matrix elements at specific wavelengths and scattering angles, enough information in many cases to enable discrimination among a wide variety of different particles. This can be of considerable clinical significance in the case of biological particles and considerable industrial significance in the case of other types of particles. Measurement of a sufficient number of polarization related phenomena to extract the ten independent Mueller matrix elements would be a formidable task involving many experimental configurations and difficult measurements. However, it is now known that this task can be simplified by deriving all of the relevant information from the measurement of a single intensity using a single apparatus.
Apparatus of this type for identifying biological particles is disclosed in pending U.S. patent application Ser. No. 180,686, filed on Apr. 8, 1988, and entitled BIOLOGICAL PARTICLE IDENTIFICATION APPARATUS, this pending application being a continuation of application Ser. No. 893,074, filed on Aug. 1, 1986.
Nevertheless, it has heretofore been considered necessary to derive such information with respect to at least eight matrix elements. When a substance is to be identified by comparing the values derived for this number of matrix elements with values associated with known substances, a substantial quantity of data must be stored and the data processing required to arrive at an identification is both complex and time consuming.